1. Field of the Invention
This invention relates to an apparatus and method for forming a fibrous structure from a stream of fluid-entrained fibers. More specifically, this invention relates to an apparatus and method for forming a fibrous structure having a greater width than that of a fluid-fiber stream directed to a forming surface upon which the fibrous structure is formed.
2. Description of the Prior Art
In commerical web forming operations it is highy desirable to increase product output to thereby minimize the unit cost of manufacturing. This is particularly important when manufacturing single and limited use fibrous products, such as cosmetic pads, industrial towels, household towels, facial tissues, impregnated wipes, components of disposable diapers and sanitary napkins, and the like. These products must be economically manufactured so that they can be sold profitably at a price that is low enough to justify their frequent disposal.
One way of increasing product output in a web forming operation is to form the web several times wider than the desired width of the final product. The fibrous web can then be severed in laterally spaced-apart regions to form more than one final product from the initially formed web. This technique for increasing product output can be advantageously employed in the formation of single and limited use air-laid products that are intended to compete with products that are made by faster wet-forming processes.
Apparatus employed to form air-laid webs generally include a fiberizing device, such as a fiberizing roll, for separating fibers from a fibrous feed lap or mat and entraining the fibers in air to form an air suspension of the fibers. The air suspension of fibers is then directed through an upstream end of a conveying duct toward a moving foraminous forming surface which intercepts a downstream open end of the duct. The air from the suspension is directed through the forming surface, and the fibers are condensed upon the surface to form the air-laid fibrous web. Most preferably, a partial vacuum is established behind the forming surface to aid in directing the suspension of fibers toward the forming surface to form the web. Quite often the formed web is subjected to post-treatment operations; such as embossing, adhesive bonding and the like; to impart desired properties to said webs, and ultimately to the finished product.
It has been suggested in the prior art to increase the width of web formation by employing flow-spreading duct work having diverging sidewalls to increase the width of fiber flow. In order to aid in the flow spreading function prior art flow-spreaders have included laterally spaced-apart vanes, flow throttling diaphragms and similar structures to attempt to maintain lateral uniformity of the flow as it is spread. These techniques have not been entirely satisfactory, and nonuniformities of flow created by the lateral spreading operation have been manifested in undesirable basis weight variations across the width of the formed fibrous structures. Accordingly, it is believed to be highly desirable to accomplish the flow spreading function with a minimum of lateral movement of the air-suspension of fibers. The instant invention provides such a function.
Air-forming apparatus and methods for forming fibrous webs of varying widths are also known in the prior art. For example, see U.S. Pat. Nos. 3,753,271, issued to McBean and 3,844,751, issued to Stewart. Both of these latter patents provide for the variable orientation of a conveying duct relative to a forming wire to vary the width of the formed web. However, in accordance with the techniques disclosed in both of these prior art patents, the width of the formed fibrous structure can be no greater than the maximum spacing between laterally spaced-apart walls of the conveying duct through which the fibers are conveyed. Therefore, if it is desired to form a web having a greater width than the maximum dimension of the forming duct, it is necessary to utilize multiple air-forming devices in combination with each other, as disclosed in the Stewart patent. Obviously it would be simpler and more economical to achieve wide web formation with a single air-forming device, as opposed to multiple devices.
In the U.S. Pat. No. 3,753,271 to McBean, a fiberizing roll is rotated at a relatively high speed to separate fibers from a feed mat. The axial dimension of the fiberizing roll in the McBean device must be close to the maximum web width that one desires to form on the apparatus. However, the larger the roll employed, the more cumbersome and expensive the equipment becomes. Therefore, it is highly desirable to be able to reduce the width of the fiberizing roll without sacrificing web width. The instant invention is directed to a method and apparatus which can be employed to achieve this objective.